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. i 3 a P" Patented June l t, ltl l'.

FROCESS FOE, Z

GERMANY, A- r, a con- PREEEAEATION G3? IVIAGNESIUIVL CHROMATES.

I-To'Jrawing. itpplicatien filed June 3, 132-5. Serial No. 113,552, and in Germany .Tune 22, 1925.

,es to tae preparation This invention of magnesium chromates.

leretoi cre no eei preparation of 11'! been disc process for the chroinates preparation from .uic acid Dammer Tel.

et be con 'ed as such,

"ion 0 compcsiti metal or alkaline ear ch in formation of double salts can b its.

magnesiur'- cl such acidfor double, decomposition as to u the alkali metals or the alkaln. wth metals which are more diliieultly soluble in water than magnesitun chromates. The double decomposition is carried out in such. a way tl both salts react with each other in the presence of water. The reaction conditions are so chosen that the more difiicultly soluble alkali metal alkaline earth metal salt, as the case may be, sepa out while the magnesium ehromate remains in solution; In the case of alkaline earth metal chromates, these conditions satisfied by treating their aqueous solutons with aqueous solutions of magiiesiun'i sulphate at a boiling temperature. Tn the case of alkali'metal chromates, the double decor position reaction of the aqueous solutions of the two components is carried out in a par ial vacuum at the lowest possible temperature. First, the greater part of the alkali metal salt is precipltatec, and then the magnesium chremate separates out. Therefore the precipitated salt is first filtered off and then the solution is further evaporated until all or the magnesium chromate separates out. The concentrated solutions of the magnesium chromate may be utilized directly without evaporation for many purposes.

The process ot this invention is very important commercially since the magnesium chromate which is produced possesses a large number of advantages over the chromates heretofore known. Among other advantages, the ma nesium chromate produced by this inve 1011 possesses that of very great solubility and an advantage which is very important in oxidation procof organic chemis 'ry, in that on reduction it produces salts which are very soluble. Another advantage is th cheapness of the magnesium salt as compared with alkali metal salts.

This invention is illustrated by the following emniples:

1.100 parts of calcium chromate are re. out in the form of strong yellow mono-clinic prisms. I

2. The reaction can be hastened and the consumption of solvents diminished by operatng under pressure at ten'iperatures above 100 C. Also in this way the dissolving of gypsum in disturbing amounts can be avoided.

3. 171 parts by weight of crystalline sodium chromate are dissolved hot in an equal amount of water and 100 parts of crystalline magnesium chloride dissolved in 100 parts of water; The two solutions are mixed and evaporated inavacuum about 30-85", it being preferable to allow the sodium chromate solution to run slowly into the magnesium chloride solution during the vacuum distillation. Very soon sodium chloride separates out in crystalline form. As soon as the formation of magnesium chromate crystals sets in, the reaction is interrupted, the mixture is filtered, and the filtrate is further evaporated. immediately magnesium chromate begins to crystallize outwith only very small amounts of sodium chloride. It is obtained perfectly pure by recrystallization from a concentrated solution.

l. The double decomposition with magnesium sulphate is carried out in the same way. Equi-n'iolecular concentrated solutions of sodium chromate or potassium chromate and magnesium sulphate are mixed and a saturated solution of 50 parts of crystalline magnesium chloride and the solution is evaporated in a vacuum at a temperature which is not allowed to 0 above 40 C. After most of the sodium giloride has sepa:

rated out, the mixture is filtered while warm on a suction filter which has reviously been warmed. The filtrate solidifies in the cold to a aste of magnesium bichromate crystals.

OF course, the process can also be carried out in such a way that magnesium bichromate and sodium bichromate are produced at the same time. One method of carrying out this rocess commercially isb mixing sodium cliromate with the require amount of sulphuric acid and magnesium sulphate, carrying out the double decomposition in the warmth, separating the solution of magnesium bichromate from the precipitated sodium sulphate by suction filtering after the .mixture has cooled, and then subsequently washing the paste of sodium sulphate cr stals with a small amount of concentrate magnesium sulphate solution.

It is not necessary to exercise as much care to keep the temperatures low in the case of the double decomposition of alkali metal bichromates with magnesium salts as in the case of the preparation of neutral chromates, because in the former case the tendency for double salts to form is not as reat.

g In the appended claims by the term alkali-forming metal we mean a metal of the alkali or alkaline earth groups.

We claim:

1. A process of preparing magnesium chromates which comprises reacting a chromate of an alkali-forming metal with a magnesium salt of an acid which forms with the alkali-forming metal a salt which is more difficultly soluble in water than the magnesium chromate.

2. A process of preparing magnesium chromatcs which comprises reacting in the presence of water a chromate of an alkaliformin metal with a magnesium salt of an acid w ieh forms with the alkali-forming metal a salt which is more difiicultly soluble in water than the magnesium chromate.

3. A process of preparing a magnesium ehromate which comprises reactin a chromate of an alkaline earth metal wit a magnesium salt of an acid which forms with an alkaline earth metal a salt which is more difiicultly soluble in water than the magnesium chromate.

4. A process of preparing magnesium chromate, which comprises reacting a monochromate of an alkali-forming metal with a magnesium salt of an acid which forms with an alkali-forming metal a salt which is more diflicultly soluble in water than the magnesium chromate.

5. A process of preparing magnesium chromate, which comprises reacting in the presence of water a monochromate of an alkali-forming metal with a magnesium salt of an acid which forms with an alkali-forming metal a salt which is more ditficultly soluble in vater than the magnesium chromate.

6. A process of preparing a magnesium chromate, which comprises reacting a monochroinatc of an alkaline earth metal with a magnesium salt of an acid which forms with an alkaline earth metal a salt which is more difiicultly soluble in water than the magnesium chromate.

7. A process of preparing a magnesium chromate, which comprises reactin a calcium chromate with ma nesium sulfate in a hot aqueous solution and separating the calcium sulfate so formed from the reaction mixture.

8. A process of preparing magnesium chromate, which comprises reacting calcium monochromate with magnesium sulfate in a hot aqueous solution and separating the calcium sulfate so formed from the reaction mixture.

In testimony whereof, we affix our signatures.

GEORG KRANZLEIN. ARTHUR VOSS. 

